It is well known to launder fabrics in automatic washing machines. A standard automatic washing machine operation includes at least one wash cycle (and in some cases more than one wash cycle), a spin cycle which removes significant proportions of the washing liquor from the wash cycle and a final rinse cycle.
Cleaning agents such as surfactants and detergent builders are commonly added to the washing machine drum in the wash cycle to assist in the mechanical removal of soil and stains from fabrics.
It is also known to add additional materials, in particular fabric care benefit agents such as softeners, feel modifiers and anti-wrinkle agents, during the rinse cycle and not during the wash cycle, in order to avoid interference from other components present in the wash liquor during prior stages of the laundering operation. Certain of these materials are required to be deposited on the fabric in order to give the maximum benefit. This applies, for instance, to perfumes, brightening agents, fabric care benefit agents and soil release agents. It would be desirable to maximize the potential for deposition of these materials on the fabric when added to the rinse cycle.
The pH of the aqueous wash liquor during the wash cycle is generally high, in particular above 7 and most commonly at least 9, often in the range 10.5 to 12.5, and sometimes higher. Due to the different nature of additives commonly included in the rinse cycle and the removal of the majority of the wash liquor, the pH of the rinse liquor is generally lower than that in the wash cycle but is not usually below 7.
It has been known to rinse laundry with a solution or rinse bath having a pH below 7, but this has not been done in the context of automatic washing machine processes. Automatic washing machine processes have special requirements in that it is usual to include a complex detergent composition in the wash cycle and it is common to include a variety of fabric types in a single wash.
In particular, manufacturers of laundry washing compositions are constantly striving to improve the properties of such compositions while retaining a composition which is technically and economically attractive. In particular, removal of greasy stains and removal of bleachable stains is an aspect which generally requires improvement but the types of component of a laundry washing composition which improve such performance tend to be some of the more expensive components, such as bleach components. Therefore it would be desirable to provide means by which these problems could be addressed without the necessity to increase the level of expensive components.
A problem which occurs with automatic washing machine processing is one of gradual residue deposition on the laundry over a number of washes. This residue can lead to a gradual dulling of dark colored fabrics or generally inducing a “dingy” appearance in white or other pale fabrics. It also makes removal of stains from the surface of the fabric on which the residue has deposited more difficult. Again, it would be desirable to provide methods for addressing these problems without necessarily requiring expensive components in the laundry washing composition.